Aerial lifts are frequently employed for lifting operatives to elevated working sites, for example to install overhead pipe work during building construction. A typical aerial lift may comprise a mobile elevated work platform (MEWP) having an extendable boom which has an elevator basket or cage for housing operatives securely to the end of the boom. Alternative aerial lifts may comprise a MEWP having an extendable scissor lift which has an elevator basket or cage for housing operatives securely to the end of the scissor lift.
The basket or cage generally contains a control panel which permits an operative standing in the basket or cage to manoeuvre the work platform as desired. The aerial lift may be powered using hydraulics powered by the MEWP's engine.
The control panel generally features an emergency stop switch and a safety switch which needs to be operated before the controls can be operated. In boom lifts the safety switch is typically a footswitch which must be depressed to activate the controls. In scissor lifts the safety is typically a dead man's handle. If the safety switch is release, the basket of cage is prevented from moving immediately but the MEWP's engine (which powers the hydraulics) continues to run. If the emergency stop switch is activated then both the basket is prevented from moving and the MEWP's engine is stopped.
Unfortunately it is known that operators can become trapped between the basket and an obstacle before they can either release the safety switch or activate the emergency stop. This is known as an entrapment event. Accidents of this nature can be fatal.
The present applicants have previously described a safety device designed to limit the damage caused by entrapment events by detecting such an event after it happens and preventing further movement of the basket or cage. The safety devices comprise either a tensioned cord or wire (EP2096078B1) or an a pressure sensitive safety edge (WO2012/001353). Activation of the safety device, which is located proximate to the control panel, prevents movement of the basket or cage by overriding the safety switch.
The present inventors have identified that it is preferable to prevent an entrapment even before it occurs rather than after it happens. Therefore it is an objective of the present disclosure to provide a pre-crush module that can prevent entrapment events before they happen.